Character constant
From cppreference.com
Syntax
'c-char '
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(1) | ||||||||
u8'c-char '
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(2) | (since C23) | |||||||
u'c-char '
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(3) | (since C11) | |||||||
U'c-char '
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(4) | (since C11) | |||||||
L'c-char '
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(5) | ||||||||
'c-char-sequence '
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(6) | ||||||||
L'c-char-sequence '
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(7) | ||||||||
u'c-char-sequence '
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(8) | (since C11)(removed in C23) | |||||||
U'c-char-sequence '
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(9) | (since C11)(removed in C23) | |||||||
where
- c-char is either
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- a character from the basic source character set minus single-quote (
'), backslash (\), or the newline character. - escape sequence: one of special character escapes \' \" \? \\ \a \b \f \n \r \t \v, hex escapes \x... or octal escapes \... as defined in escape sequences
- a character from the basic source character set minus single-quote (
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(since C99) |
- c-char-sequence is a sequence of two or more c-chars.
1) single-byte integer character constant, e.g. 'a' or '\n' or '\13'. Such constant has type int and a value equal to the representation of c-char in the execution character set as a value of type char mapped to int. If c-char
2) UTF-8 character constant, e.g. u8'a'. Such constant has type char8_t and the value equal to ISO 10646 code point value of c-char, provided that the code point value is representable with a single UTF-8 code unit (that is, c-char is in the range 0x0-0x7F, inclusive). If c-char
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3) 16-bit wide character constant, e.g. u'่ฒ', but not u'๐' (u'\U0001f34c'). Such constant has type char16_t and a value equal to the value of c-char in the 16-bit encoding produced by mbrtoc16 (normally UTF-16). If c-char
4) 32-bit wide character constant, e.g. U'่ฒ' or U'๐'. Such constant has type char32_t and a value equal to the value of c-char in in the 32-bit encoding produced by mbrtoc32 (normally UTF-32). If c-char
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(until C23) |
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3) UTF-16 character constant, e.g. u'่ฒ', but not u'๐' (u'\U0001f34c'). Such constant has type char16_t and the value equal to ISO 10646 code point value of c-char, provided that the code point value is representable with a single UTF-16 code unit (that is, c-char is in the range 0x0-0xD7FF or 0xE000-0xFFFF, inclusive). If c-char
4) UTF-32 character constant, e.g. U'่ฒ' or U'๐'. Such constant has type char32_t and the value equal to ISO 10646 code point value of c-char, provided that the code point value is representable with a single UTF-32 code unit (that is, c-char is in the range 0x0-0xD7FF or 0xE000-0x10FFFF, inclusive). If c-char
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(since C23) |
5) wide character constant, e.g. L'ฮฒ' or L'่ฒ. Such constant has type wchar_t and a value equal to the value of c-char in the execution wide character set (that is, the value that would be produced by mbtowc). If c-char is not representable or maps to more than one wide character (e.g. a non-BMP value on Windows where wchar_t
6) multicharacter constant, e.g. 'AB', has type int
7) wide multicharacter constant, e.g. L'AB', has type wchar_t
8) 16-bit multicharacter constant, e.g. u'CD', has type char16_t
9) 32-bit multicharacter constant, e.g. U'XY', has type char32_t
Notes
Multicharacter constants were inherited by C from the B programming language. Although not specified by the C standard, most compilers (MSVC is a notable exception) implement multicharacter constants as specified in B: the values of each char in the constant initialize successive bytes of the resulting integer, in big-endian zero-padded right-adjusted order, e.g. the value of '\1' is 0x00000001 and the value of '\1\2\3\4' is 0x01020304
In C++, encodable ordinary character literals have type char, rather than int
Unlike integer constants, a character constant may have a negative value if char is signed: on such implementations '\xFF' is an int with the value -1
When used in a controlling expression of #if or #elif
16/32-bit multicharacter constants are not widely supported and removed in C23. Some common implementations (e.g. clang) do not accept them at all.
Example
Run this code
#include <stddef.h> #include <stdio.h> #include <uchar.h> ย int main (void) { printf("constant value \n"); printf("-------- ----------\n"); ย // integer character constants, int c1='a'; printf("'a':\tย %#010x\n", c1); int c2='๐'; printf("'๐':\tย %#010x\n\n", c2); // implementation-defined ย // multicharacter constant int c3='ab'; printf("'ab':\tย %#010x\n\n", c3); // implementation-defined ย // 16-bit wide character constants char16_t uc1 = u'a'; printf("'a':\tย %#010x\n", (int)uc1); char16_t uc2 = u'ยข'; printf("'ยข':\tย %#010x\n", (int)uc2); char16_t uc3 = u'็ซ'; printf("'็ซ':\tย %#010x\n", (int)uc3); // implementation-defined (๐ maps to two 16-bit characters) char16_t uc4 = u'๐'; printf("'๐':\tย %#010x\n\n", (int)uc4); ย // 32-bit wide character constants char32_t Uc1 = U'a'; printf("'a':\tย %#010x\n", (int)Uc1); char32_t Uc2 = U'ยข'; printf("'ยข':\tย %#010x\n", (int)Uc2); char32_t Uc3 = U'็ซ'; printf("'็ซ':\tย %#010x\n", (int)Uc3); char32_t Uc4 = U'๐'; printf("'๐':\tย %#010x\n\n", (int)Uc4); ย // wide character constants wchar_t wc1 = L'a'; printf("'a':\tย %#010x\n", (int)wc1); wchar_t wc2 = L'ยข'; printf("'ยข':\tย %#010x\n", (int)wc2); wchar_t wc3 = L'็ซ'; printf("'็ซ':\tย %#010x\n", (int)wc3); wchar_t wc4 = L'๐'; printf("'๐':\tย %#010x\n\n", (int)wc4); }
Possible output:
constant value -------- ---------- 'a': 0x00000061 '๐': 0xf09f8d8c ย 'ab': 0x00006162 ย 'a': 0x00000061 'ยข': 0x000000a2 '็ซ': 0x0000732b '๐': 0x0000df4c ย 'a': 0x00000061 'ยข': 0x000000a2 '็ซ': 0x0000732b '๐': 0x0001f34c ย 'a': 0x00000061 'ยข': 0x000000a2 '็ซ': 0x0000732b '๐': 0x0001f34c
References
- C17 standard (ISO/IEC 9899:2018):
- 6.4.4.4 Character constants (p: 48-50)
- C11 standard (ISO/IEC 9899:2011):
- 6.4.4.4 Character constants (p: 67-70)
- C99 standard (ISO/IEC 9899:1999):
- 6.4.4.4 Character constants (p: 59-61)
- C89/C90 standard (ISO/IEC 9899:1990):
- 3.1.3.4 Character constants
See also
C++ documentation for Character literal
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